1. Field of the Invention
This invention relates to pipe swivel joints, and more particularly, to such swivel joints with multiple flow passageways for the simultaneous transfer of a plurality of separate fluids.
2. Description of the Prior Art
The production of oil and gas from offshore wells has developed into a major endeavor of the petroleum industry, and this growth has led to the development of various means for transporting petroleum and its products from offshore locations to shore-based refineries or storage facilities. Many of these wells are now being drilled and completed in deepwater where the use of marine tankers of very large capacity constitutes the most practical and efficient transport method.
One of the facilities which is employed in such a tanker operation is an offshore loading production ship or other floating terminal having a plurality of storage tanks for receiving and storing petroleum products from the deepwater wells. Shuttle tankers are used to receive the stored petroleum fluids and gas for transportation to the shore-based refineries. A production ship includes pipes or hoses extending from the ship to a floating buoy. A riser extends downward from the buoy to a riser base on the sea floor, and flowlines extend from the riser base to a plurality of production wells. The production ship is anchored in position about the riser, but the ship is free to revolve about the riser to head into winds and ocean currents to minimize the load acting on the mooring device. The riser may be coupled to several sources of gas and petroleum fluids that may be loaded simultaneously through a plurality of conduits all of which are connected to a single, multiple-conduit coaxial swivel joint on the floating buoy.
The multiple-conduit swivel joint has two or more annular chambers each communicating with an inlet and a corresponding outlet to provide two or more separate and distinct flow paths, and although such devices provide the desired function they are relatively complex and thus difficult and expensive both to manufacture and to disassemble for service. Some of the prior art multiple-conduit swivel joints include a plurality of stages of gradually decreasing diameter stacked one on top of the other in a stair step manner. Such an arrangement is satisfactory when only a few stages are needed, but cannot be used with a large number of stages as the diameter of the stages at the top and bottom of the joints become very small and very large respectively. Also such prior art swivel joints cannot be used for high pressure service due to failure of seals used between annular inner and outer joint members. Multiple-conduit swivel joints having a plurality of equal diameter stages are difficult to assemble and disassemble.
What is needed, therefore, is a large-diameter coaxial swivel joint that has a plurality of separate and distinct fluid flow passages between a plurality of inlets and a plurality of outlets, that is relatively uncomplex in design and thus inexpensive to manufacture and that is easy to assemble and disassemble for cleaning and maintenance. It is also important that such a swivel joint withstand higher pressures and contain more stages than the prior art joints.